Process for removing elemental sulfur with hydrazine



United States Patent Ofiice PROCESS FOR REMOVING ELENIENTAL SULFUR WITH HYDRAZINE Ray T. Wendland, Pittsburgh, Pa., assignor to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Application June 19, 1958 Serial No. 743,023

9 Claims. (Cl. 208-236) This invention relates to a novel method for removing elemental sulfur from hydrocarbon liquids.

It is frequently desired to remove elemental sulfur from hydrocarbon liquids containing it. For example, the presence of elemental sulfur in crude petroleum oils is highly objectionable. One objection is its action on various metals leading to corrosion of pipelines, storage vessels and distillation facilities in general. Another objection to this type of sulfur is that it can be the source of malodorous and otherwise undesirable sulfur compounds. These undesired sulfur compounds may be formed upon distillation, cracking and other similar crude processing requiring temperatures on the order of 250 F. and above, during which the elemental sulfur readily reacts with the petroleum hydrocarbons to yield objectionable sulfur compounds.

It has now been found that elemental sulfur can 'be readily removed from hydrocarbon liquids by means of hydrazine. By hydrocarbon liquids is meant relatively pure hydrocarbon liquids such as benzene, and liquids composed predominantly of hydrocarbons or mixtures of hydrocarbons such as petroleum oil and products derived from coal and other bitumens. Thus, by means of the present invention, hydrazine can be employed to remove substantially all of the elemental sulfur present in a crude petroleum oil in which the presence of elemental sulfur is especially undesirable.

In accordance with the present invention, the elemental sulfur content of sulfur-containing hydrocarbon liquids as for example, a crude petroleum oil, is removed by contacting the oil with hydrazine. The hydrazine employed can be either anhydrous hydrazine or aqueous hydrazine solutions containing as much as 50 percent water. By anhydrous hydrazine is meant hydrazine containing less than about 4 percent of water. Anhydrous hydrazine and aqueous solutions thereof are not miscible with hydrocarbons to any appreciable extent. Due to the immiscibility of hydrazine with the hydrocarbon liquids, it is essential that the treating operation be accompanied by mixing or other means of agitation to insure a thorough mingling of the hydrazine and sulfur with consequent substantially complete removal of the undesired sulfur. In addition various known solutizing or emulsifying agents can be employed to achieve the desired commingling of the reactants. Upon contacting an elemental sulfur-containing hydrocarbon liquid, the hydrazine combines readily with the elemental sulfur to form mainly hydrogen sulfide and nitrogen according to the following equation:

The nitrogen and hydrogen sulfide products resulting from the chemical reaction between the sulfur and hydrazine are liberated from the treated hydrocarbons in the form of a gas and disposed of in any suitable manner.

. Patented Mar. 29, 1960 settling or by centrifugation. It is sometimes desirable to employ water washing of the separated hydrocarbon phase after treatment thereof with hydrazine. This is to insure removal of substantially all of the hydrazine. When aqueous hydrazine solutions are employed in the treatment of crude petroleum oils, the two phases are sometimes in the form of a rather stable emulsion. Such emulsions can be broken upon long standing or upon the addition of emulsion breaking agents or by centrifuging. An alternative procedure for the separation and recovery of the excess hydrazine from treated crude oils is simply to distill the mixture and recover the hydrazine as a distillate. For example, hydrazine is mixed with a crude petroleum oil containing elemental sulfur and the mixture is heated. The hydrazine reacts with the elemental sulfur to form nitrogen and hydrogen sulfide which products are liberated as gases at temperatures above about 50 C. As the temperature increases to density, the hydrazine is readily separable from any light naphtha which may be present in the distillate.

The treatment of a liquid hydrocarbon or hydrocarbon mixture such as a crude petroleum oil with hydraz ine for the removal of elemental sulfur can be effected at atmospheric pressure and at ambient temperatures. The rate of reaction between the sulfur and hydrazine increases with temperature and for this reason it is preferred to employ elevated temperatures. However, to insure liquid phase operation, the temperatures employed should not exceed the boiling point of either the hydrazine treating agent or the hydrocarbon charge. The boiling point of anhydrous hydrazine (96 percent) is approximately 114 C. and for aqueous hydrazine solutions is somewhat higher. At temperatures below about 50 C. the hydrogen sulfide which is formed in the treating operation combines with the excess hydrazine which may be present to form a hydrazinium salt according to the following equation: i

of sulfur present, the temperature at which the treating operation is conducted, amount of hydrazine employed, the efliciency of the apparatusand other factors. Thus,

the time of treatment varies widely and ranges from as; low as several minutes up to 24 hours or more. 'The' hydrocarbon liquids undergoing treatment experience no adverse effects due to contact with hydrazine and therefore, the upper time limit is governed only byp'ractical considerations In general, contact times ranging from about 15 minutes to about 24 hours or more, are sum.

cient for substantially complete removal of elemental sulfur.

The amount of hydrazine utilized in accordance with the present invention, is the amount theoretically required to react with. all of the elemental sulfur present in the hydrocarbon feed. Since the percentage of sulfur in any. given quantity .of hydrocarbon liquid can be readily determined, suitable amounts of hydrazinel areused to properly combine with the sulfur to form hydroresults of treating a number of hydrocarbons for the gen sulfide. However, it is preferred to employ an eX- removal of elemental sulfur.

Table Weight Percent Elemental Sulfur, Time, Treating A gent Weight Tcmper- Elemen- Sample Sample, Percent by Weight Hours Treating ature, tal Sulgrams Agent, C. fur Regrams moved 0. Goldsmith Crude so 96% hydrazine 4 2s-32 90 6.0 97 22.0 99.5

0 0. 5 87 l. O 92 McElroy Crude 80 2.0 do 4 28-32 95 3. 0 96 8. 0 98 24. 0 93 Heavy Kentucky Crude 70 g }04% hydrazine"-.. 4 90-100 "5,6 Same Heavy Kentucky 0 Crude. 2 4 110 125 Q8 Topped McElroy Crude.. 109 1 g hydrazine-nu 4 90400 i "iii Solution of Sulfur in Am '1 0 Benzene 00 1 96% liyd1azlnc. l 2 99 Solution of Sulfur in Xylene. 100 2 }64% hydrnziue 6 100 G47 hydrazine l0 i'tittttllfsl-"l 0 Topped McElroy Crude. 100 Sodium hydroxide.

2.10 Combined 3 99 0.001 Elemental cess of hydrazine as this has been found to effectively increase the rate of sulfur removal. A large excess of hydrazine can be employed, as hydrazine has no deleterious effect on hydrocarbons and the upper limit is governed solely by cost considerations.

For the removal of elemental sulfur in accordance with the invention, contact of the elemental sulfur-containing hydrocarbons with hydrazine can take place in batchwise fashion employing conventional apparatus known to the art which is adapted to provide good agitation in the mixture, or in continuous countercurrent contact apparatus such as is used, for example, in liquidliquid extraction processes. Similarly, the separation and recovery of the excess hydrazine by phase separation can be accomplished batchwise simply by settling or continuously by employing centrifugal separators, or time settling tanks.

As indicated previously, anhydrous hydrazine or aqueous solutions of hydrazine containing varying amounts of water can be utilized for the removal of elemental sulfur in accordance with this invention. As is to be expected, the efficiency of the sulfur removal is greater with the concentrated or anhydrous hydrazine. However, it has been found that the efficiency of aqueous hydrazine solutions can be materially improved by the use of sodium hydroxide with the hydrazine solution. In this embodiment of the invention, sodium hydroxide is added to the aqueous hydrazine solution and the treating operation is conducted at an elevated temperature. Preferably, the temperature employed ranges from about 60 C. up to about 100 C. Sodium hydroxide is employed in an amount to provide 1 to 2 mols sodium hydroxide for each mole of water present with the hydrazine. By means of this procedure, the efficiency of aqueous hydrazine solutions is materially improved and approaches that obtained by the use of anhydrous hydrazine. A further advantage of this embodiment of the invention is that the organically combined sulfur content, if any, of the oil is materially reduced.

The cfiicacy of hydrazine for the removal of elemental sulfur has been demonstrated in the laboratory by a number of tests wherein hydrocarbon liquids containing elemental sulfur were treated in accordance with the invention. The following table gives the conditions and The data in the above table shows the remarkable effectiveness of hydrazine for removing elemental sulfur.

It is apparent that our invention provides an effective method for the control and removal of sulfur from sulfurcontaining hydrocarbon liquids such as crude petroleum oils. The removal of such corrosive sulfur leads to advantages in the handling and further processing of the oil in that corrosion of equipment due to elemental sulfur is substantially eliminated. Maintenance costs are therefore considerably reduced. A further advantage of the process of the invention is that ordinary refinery contact apparatus can be used in the processing and streams of crude petroleum oil can be processed as they arrive from pipe lines and storage tanks.

While the invention has been described primarily in relation to the treatment of crude petroleum oils containing elemental sulfur, it is within the scope of the invention to treat any hydrocarbon liquid from which it is desired to remove elemental sulfur. Thus, for example, the benefits of the invention are obtained in the treatment of fractions of a crude petroleum oil containing elemental sulfur as may be obtained by such processes as chromatographic fractionation, thermal diffusion and the like, in which processes the heating of the crude petroleum oil is insufficient to cause reaction of the elemental sulfur with petroleum hydrocarbons. Similarly, the invention can be advantageously employed for the removal of elemental sulfur from relatively pure hydrocarbons such as benzene, toluene and the like.

Those modifications and equivalents which fall within the spirit of the invention and the scope of the appended claims are to be considered part of the invention.

1 claim:

1. A process for removing elemental sulfur from hydrocarbon liquids which comprises contacting the hydrocarbon liquid with hydrazine to effect reaction between the said sulfur aud said hydrazine.

2. The process of claim 1, wherein contact of the hydrocarbon liquid is carried out at an elevated temperature but at a temperature below the boiling point of the hydrazine treating agent and the hydrocarbon liquid.

3. The process of claim 1, wherein contact of the hydrocarbon liquid is carried out at a temperature above about 50 C. but below the boiling point of the hydrazine treating agent and the hydrocarbon liquid.

4. The process of claim 1 wherein the hydrocarbon liquid is a petroleum oil.

5. The process of claim 1, wherein the hydrocarbon liquid is a crude petroleum oil.

6. The process of claim 1, wherein the hydrocarbon liquid is contacted with an aqueous hydrazine solution in the presence of sodium hydroxide.

7. A process for removing elemental sulfur from a petroleum oil which comprises contacting the oil with hydrazine for a time and in an amount in excess of that required to combine with the elemental sulfur present in the oil, said contact being carried out with continuous agitation, and then separating the excess hydrazine from the treated oil.

8. A process for removing elemental sulfur from a petroleum oil which comprises contacting thte oil with hydrazine for a time and in an amount in excess of that required to combine with the elemental sulfur present in the oil, said contact being carried out with continuous agitation, heating the mixture of hydrazine and oil to liberate hydrogen sulfide, and then separating the excess hydrazine from the treated oil. I

9. A process for removing elemental sulfur from a 5 petroleum oil which comprises contacting the oil with 10 hydrazine distillate.

References Cited in the file of this patent Ephraim: Inorganic Chemistry, Interscience Pub. Inc., N.Y.C., 5th edition, revised; 1949, page 668, lines 15 41-, page 669', lines 1-10.

Audricth et a1.: The Chemistry of Hydrazine, John Wiley & Sons, Inc., N.Y.C., 1951,. pages 199-200. 

1. A PROCESS FOR REMOVING ELEMENTAL SULFUR FROM HYDROCARBON LIQUIDS WHICH COMPRISES CONTACTING THE HYDROCARBON LIQUID WITH HYDRAZINE TO EFFECT REACTION BETWEEN THE SAID SULFUR AND SAID HYDRAZINE. 